'We have a suspect in custody'

As their photographs spread rapidly across the internet, the Tsarnaev brothers decided to move. Not waiting for police to find them, they gathered guns and homemade explosives for what became a final, bloody rampage on a community still in shock from the bombings three days before.

Law enforcement officials had hoped a wide distribution of photos would bring clues. Instead, it appears to have jarred the Tsarnaevs into action. After apparently spending three days watching the aftermath of the bombings from nearby Cambridge, the brothers left their apartment within hours of the FBI news conference, heavily armed and prepared for a fight.

Just after 10.30pm on Thursday Boston time (12.30pm Friday Sydney time), the two men walked up to a parked police car at the Massachusetts Institute of Technology, where Sean Collier, a 26-year-old campus officer, was nearing the end of his shift. Abruptly, one of the men was seen pulling a gun and shooting Collier multiple times, including once in the head. Some officers concluded the shooting was an effort to provoke a larger confrontation with police.

Search: Law enforcement agents look around the corner of a house where Boston Marathon bombing suspect Dzhokhar Tsarnaev was believed to be hiding in Watertown, Massachusetts. Photo: Reuters

Collier was found in his car by other police and taken to a hospital, where he was pronounced dead.

Advertisement

At 10.39pm, just blocks from where Collier lay bleeding, the men held up the driver of a Mercedes SUV. They drove the hijacked car through Cambridge to nearby Watertown, where they searched for bank machines.

''They tell [the driver] they're the bombers,'' said a law enforcement official familiar with the account given by the SUV's owner, who was released unharmed after a 30-minute ordeal.

An FBI officer stands in front of the boat at 67 Franklin St. where Dzhokhar Tsarnaev, was hiding inside. Photo: Reuters

The Tsarnaevs stopped at three ATMs and withdrew $800 cash from one, using the SUV owner's bank card. Denied cash at other ATMs, the suspects dropped off the vehicle owner at a petrol station. ''The guy was very lucky that they let him go,'' Massachusetts State Police spokesman David Procopio said.

Just after midnight, police saw the Mercedes and gave chase. The SUV tore through Watertown with as many as a dozen police cars in pursuit. The officers had to dodge homemade bombs hurled from the speeding Mercedes.

At 12.50pm, the SUV stopped in a residential neighbourhood in Watertown. The brothers opened fire, igniting a gun battle witnessed by neighbours peering from houses.

After more than 200 rounds were traded over several minutes, some officers were out of ammunition and charged the brothers' position with their police car. A witness saw one of the shooters toss a metallic object - possibly a pressure-cooker bomb similar to the ones used in the marathon attack - in the direction of the police line. It detonated harmlessly.

Tamerlan Tsarnaev, now out of his car, tried to lob a pipe bomb at police, but the device exploded in his hand. Police tackled and tried to subdue the amateur boxer while he was firing a pistol with the other hand.

In an apparent attempt to help his brother Dzhokhar Tsarnaev tried to ram the officers. Instead, the officers lunged out of the vehicle's path and he ran over his brother and dragged him along the street before speeding off.

Officers found the Mercedes abandoned and quickly sealed off neighbourhoods in Watertown as they began a street-by-street search for the suspect.

Tamerlan Tsarnaev was taken to a hospital where he was pronounced dead on arrival. Hospital officials said he had been shot multiple times and suffered other wounds, apparently from an explosion.

Late on Friday afternoon, authorities said they did not know Dzhokhar Tsarnaev's location. Shortly after 6pm, however, the streets of Watertown came alive with sirens.

21 Apr
Ruslan Tsarni emerged through the front door of his red-brick home in Montgomery Village, Maryland, walked down the driveway and declared to a bank of cameras that his two nephews, the accused Boston Marathon bombers, were ''losers''.

21 Apr
The world is today asking: ''How did two young ethnic Chechens come to bring bloodshed to the streets of America?'' The answer lies in the way that conflict in Russia's North Caucasus has changed from a nationalist struggle to an Islamist insurgency, connected to the ideology of global jihad.

21 Apr
The Russian FSB intelligence security service told the FBI in early 2011 about information that Tamerlan Tsarnaev, one of the brothers suspected in the Boston marathon bombings, was a follower of radical Islam, two law enforcement officials say.

21 Apr
With one suspect dead and the other captured and lying grievously wounded in a hospital, the investigation into the Boston Marathon bombings turned Saturday to questions about the men’s motives, and to the significance of an overseas trip one of them took last year.

21 Apr
A spotlight is thrown on one of the darkest corners of nationalist and Islamic militancy, to a campaign for separatism and vengeance responsible for some of the most unsparing terrorist acts of recent decades.